JPH0290616A - Through-hole forming method for interlayer insulating film - Google Patents

Abstract

PURPOSE:To enhance adhesion and to obtain a through hole having stabilized size by a method wherein an interlayer insulating film is formed by laminating a polyimide film containing no silicon on a polyimide film containing silicon, a through hole is formed by providing a small hole in the silicon-containing film and a large hole in the film containing no silicon. CONSTITUTION:A first silicon-containing polyimide film 3 is formed on the surface of a semiconductor substrate 1 containing a first wiring 2, and a second polyimide film 4, containing no silicon, is formed thereon. Then, a photoresist film 5 is formed, a window 6 is provided using a photolithographic method, the polyimide films 3 and 4 on the bottom part of the window 6 are removed by conducting a reverse reactive etching, and the window 6 is deepened into a window 6a. A window 6b is formed by removing the photoresist film 5 larger than the window 6a, a reverse reactive etching is conducted using the photoresist film 5 as a mask, and the first and the second polyimide films 3 and 4 are removed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming through holes in an interlayer insulating film of a semiconductor integrated circuit device.

[Conventional technology]

Conventionally, when forming multilayer wiring for semiconductor integrated circuit devices,
An interlayer insulating film is formed between the wiring layers to insulate them from each other.
Windows, or so-called through holes, were opened in the interlayer insulating film only in the areas to be connected, and the through holes were filled with a metal layer to connect the wiring between the layers.

Further, as this interlayer insulating film, a silicon dioxide film is usually used most often. However, when forming this silicon dioxide film, it is necessary to heat the semiconductor substrate to a fairly high temperature, and this high temperature causes minute protrusions such as hillocks on the aluminum metal vapor deposited layer, and many pins on the interlayer insulating film. There is a problem that causes holes. Also,
If a chemical vapor deposition method or the like is used to grow the interlayer insulating film to make it thick, there are problems such as cracks in the interlayer insulating film due to the difference in expansion coefficient between aluminum and aluminum. Therefore, instead of this silicon dioxide film, for example, Japanese Patent Publication No. 51-44871 proposes to use a polyimide resin layer as an interlayer insulating film. When making through holes in this polyimide resin layer, the through holes are made by an isotropic plasma etching method using oxygen plasma.

[Problem to be solved by the invention]

In the conventional through-hole forming method described above, there are local differences in film thickness due to differences in the step shape and dimensions on the surface of the base, so when forming through-holes in areas with thin film thickness, the etching time is There is a problem in that a through hole that is larger than other through holes can be opened due to the influence. Also,
Alternatively, when a through hole is formed by an anisotropic etching method, such as a reactive etching method, the cross-sectional shape of the drilled through hole becomes steep, and the adhesive strength of the metal layer that becomes the contact is weak, resulting in peeling. There is a problem that this may cause a problem of poor conductivity.

An object of the present invention is to provide a method for forming a through-hole in an interlayer insulating film, which allows a contact with an interlayer insulating film with higher adhesive strength and a through-hole with stable dimensions to be obtained.

[Means to solve the problem]

The method for forming an interlayer insulating film through hole of the present invention includes: - a first layer containing silicon on the surface of a semiconductor substrate including wiring on the main surface;
forming a second polyimide film not containing silicon overlying the polyimide film and the first polyimide film; forming a first window in the first polyimide film; forming a second window in the second polyimide film that is larger than the first window by a predetermined size and has the same central axis as the first window.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a cross-sectional view of a semiconductor chip shown in the order of manufacturing steps for explaining a first embodiment of the present invention.

In this example, L in a design rule of about 2 microns is
This is the case when applied to SI.

First, as shown in FIG. 1(a), on a semiconductor substrate 1,
A first wiring 2 made of aluminum and having a width of, for example, about 4 μm is formed by a known method.

Next, the semiconductor substrate 1 including the first wiring 2 made of aluminum is
A polyimide solution containing silicon is dropped onto the semiconductor substrate using a spin coater to form a polyimide coating film on the surface of the semiconductor substrate, and dried at a temperature of about 200°C or less in a nitrogen atmosphere to form a first polyimide film with a thickness of 0.8 μm. Next, as shown in FIG. 1(b), a polyimide solution containing no silicon is dropped onto the semiconductor substrate using a spin coater.
A polyimide coating film with a thickness of 0.8 μm is formed, the temperature is raised stepwise in a nitrogen atmosphere, and a heat treatment is performed at about 400° C. or lower to form a second polyimide film 4 with a thickness of about 1.0 μm. Next, as shown in FIG. 1(C), a layer of about 2 μm thicker than the second polyimide film 4 is coated on the second polyimide film 4.
A photoresist film 5 with a thickness of Reverse reactive etching, which is an anisotropic etching method, is performed at 5 Pa to remove the polyimide films 3 and 4 at the bottom of the window 6, thereby forming the window 6 deeply in the window 6a. Next, in Figure 1 (e
), a larger portion of the photoresist film 5 on the window 6a than the window 6a is removed by photolithography to form a window 6b. Using this photoresist film 5 as a mask, a mixed gas of carbon tetrafluoride (CF4) gas and oxygen was applied to the
Reverse reactive etching, which is an anisotropic etching method, is performed at Pa to remove the first and second polyimide films 3 and 4. At this time, only the second polyimide film 4 is etched away, and the first polyimide film 3 is not etched and retains its original shape.Next, as shown in FIG. Then, the photoresist film 5 is removed using an ordinary solvent, and a second wiring 7 made of aluminum is formed by metal vapor deposition and connected to the first wiring 2. In this way, if the windows, which are through-holes, are etched in a stepped manner, even if there are steps in the thickness of the first polyimide film, the lateral etching will not proceed, resulting in window dimensions with little variation. In addition to increasing the adhesion area between the vapor-deposited metal layer, which is the wiring, and the polyimide film, which is the interlayer insulating film, Figure 2 shows a semiconductor chip for explaining a second embodiment of the present invention. FIG. 3 is a cross-sectional view of a semiconductor chip shown in the order of steps.

This embodiment is an example in which a silicon oxide film is used in place of the photoresist film of the first embodiment. The steps in this example are:
The steps up to FIG. 1(b) of the first embodiment are the same. first,
As shown in FIG. 2(a), the semiconductor substrate temperature is heated to about 300°C in a mixed gas atmosphere of silane (SiH4) and nitrogen oxide (N20) at a pressure of about 100 Pa, plasma oxidation is performed, and a second on the polyimide film 4 with a thickness of 0.2 μm.
Next, as shown in FIG. 2(b), a photoresist film is formed on the silicon oxide film 8, and the photoresist film is selectively removed by photolithography to form a photomask. A photoresist film 5 is formed.

Next, reverse reactive etching using carbon tetrafluoride (CF4) gas as the main ingredient is performed to open windows 6C, which are through holes, in the photoresist film 5 and silicon oxide film 8.
As shown in FIG. 2(c), FIG.
) and (e), the first and second polyimide films 3 and 4 are selectively removed, and the window 6c, which is a through hole, is etched to form the window 6d.

At this time, since the lateral etching of the second polyimide film is more advanced than the other layers, large holes are formed only in the second polyimide film. The silicon oxide film 8 is removed with hydrogen (HF), aluminum is deposited by a metal vapor deposition method, and the aluminum metal vapor deposited layer is selectively etched away to form the second wiring 7 and the underlying aluminum first layer is removed. Connect to wiring 2.

Note that the photoresist film used in this example is thinner than the resist film used in the first example. The reason is usually carbon tetrafluoride (CF4
>This is because the resist film does not decrease in reverse reactive etching that uses gas as its main ingredient. Conversely, it can be said that relatively fine openings can be formed in the resist film by photolithography, so this embodiment has an advantage over the first embodiment.

In addition to the embodiments described above, as an etching mask,
In addition to photoresist films and silicon oxide films, metal films such as aluminum and titanium may also be used, and in this case, through-holes can be formed by performing reverse reactive etching using chlorine gas. . Further, in order to remove these metal films, in the case of aluminum, it is removed by immersing it in a heated phosphoric acid solution. In the case of titanium, it can be removed by soaking it in a mixture of aqueous ammonia and hydrogen peroxide.

〔Effect of the invention〕

As explained above, in the present invention, a polyimide film that does not contain silicon is layered on top of a polyimide film that contains silicon to form an interlayer insulating film, and small holes are formed in the polyimide film that contains silicon to form a polyimide film that does not contain silicon. Since we created a large through hole, the polyimide film containing silicon will not be etched in the lateral direction.
Even if there is a step difference in the thickness of this polyimide film, holes with little variation can be obtained. Further, by providing a step formed by the size of the holes in the two polyimide films, the adhesion area between the metal and the interlayer insulating film can be increased. Therefore, there is an effect that the adhesion between the interlayer insulating film and the contact can be further enhanced, and a through hole with stable dimensions can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a semiconductor chip shown in the order of manufacturing steps for explaining a first embodiment of the present invention, and FIG. 2 is a cross-sectional view of a semiconductor chip for explaining a second embodiment of the present invention. FIG. 3 is a cross-sectional view of a semiconductor chip shown in the order of steps. DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 2... First wiring, 3... First polyimide film, 4... Second polyimide film, 5...
・Photoresist film, 6.6a, 6b, 6C56d ・
...Window, 7...Second wiring, 8...Oxide film.

Claims (1)

[Claims] An interlayer insulating film formed by forming a first polyimide film containing silicon on the surface of the semiconductor substrate including wiring on one main surface, and a second polyimide film not containing silicon overlaid on the first polyimide film. forming a first window in the first polyimide film and having a predetermined size larger than the first window in the second polyimide film and having the same central axis as the first window; A method for forming a through hole in an interlayer insulating film, the method comprising the step of forming a second window.